demo.js

$('#cboCategory').change(function () {
	var categoryId = $(this).val();
	loadTypeList(categoryId);
});

function loadTypeList(categoryId) {
    $.ajax({
        type: 'POST',
        url: 'Example.aspx/GetTypeList',
        data: '{categoryId: "' + categoryId + '" }',
        contentType: 'application/json; charset=utf-8',
        dataType: 'json',
        success: function (response) {
        	loadList(response);
        },
        failure: function (response) {

        }
    });
    function rebindTypeList(data) {
        $('#cboType').get(0).options.length = 0;
        $('#cboType').get(0).options[0] = new Option('select type','');
        $.each(data.d, function () {
            $('#cboType').get(0).options[
            	$('#cboType').get(0).options.length
            ] = new Option(this.Name, this.Id);
        });
	}
}